1. Fields of the Invention
The present invention relates to a semiconductor light emitting device in which at least an active layer and a cladding layer on a substrate are made of II/VI-compound semiconductors.
2. Related Art
Since it is requested that an optical disc and a magneto-optical disc is recorded and/or reproduced with high density and high resolution, a demand for a semiconductor laser which emits green or blue laser light is more and more increased.
II/VI-compound semiconductors made of II group elements such as Zn, Hg, Cd, Mg and VI group elements such as S, Se, Te are promising as materials to form semiconductor light emitting devices such as the semiconductor lasers, light emitting diodes or the like. In particular, ZnMgSSe mixed crystal can be grown on a GaAs substrate and is suitable for a guiding layer and a cladding layer used when a blue semiconductor laser is fabricated (see "Electronics Letters 28 (1992) p. 1798").
When this kind of a II/VI-compound semiconductor light emitting device such as ZngSSe compound semiconductor is formed as the cladding layer, the GaAs substrate and the ZnSe substrate are used as semiconductor substrate on which the cladding layer and the active layer are epitaxially grown because they are excellent in crystallinity and are now commercially available on the market. In this case, in order that the semiconductor light emitting device can emit laser light with a desired short wavelength highly efficiently, the cladding layer that is eptaxially grown on the GaAs substrate directly or via a buffer layer should be formed as a compound semiconductor layer with an excellent crystallinity.
Therefore, semiconductor light emitting devices have hitherto been considered that a lattice constant of the cladding layer is strictly agreed with that of the GaAs substrate. For this reason, values x and values y of Zn.sub.x Mg.sub.1-x S.sub.y Se.sub.1-y cladding layer should be selected very strictly so that compositions cannot be selected substantially with freedom and that composition should be selected strictly. Thus, the semiconductor light emitting devices cannot be fabricated satisfactorily.
Moreover, in the II/VI-compound semiconductor light emitting devices, a p-type electrode obtained when a semiconductor laser using an electrode formed on the opposite side of the substrate, particularly, n-type substrate is fabricated generates much heat and luminous intensity is therefore deteriorated.